Question on gravitational lensing

In summary: I would recommend reading it if you are interested in this topic.Straightening out Light-bending (Mk1:3)In summary, according to gtr, "light bending" (e.g. in "gravitational lensing") does not depend on the frequency of the light being bent.
  • #1
notknowing
185
0
I was wondering whether one has examined the spectrum of gravitational lensed light (nice description on wikipedia : http://en.wikipedia.org/wiki/Gravitational_lensing ). Have there been indications on some red or blue shifts in the light from different parts of the observed ring? Does anyone know?

Rudi Van Nieuwenhove
 
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  • #2
notknowing said:
I was wondering whether one has examined the spectrum of gravitational lensed light (nice description on wikipedia : http://en.wikipedia.org/wiki/Gravitational_lensing ). Have there been indications on some red or blue shifts in the light from different parts of the observed ring? Does anyone know?

Rudi Van Nieuwenhove

I realized that I should have been more specific. What I meant is "has one observed variations in red shifts in the light from different parts of the ring ?"
 
  • #3
Are you talking about an Einstein ring? (There are a few examples of almost perfect Einstein rings which have been observed.) What kind of variations do you have in mind?
 
  • #4
As far as I know, the gravitational deflection of light should not affect light's frequency. If there are experiments showing the opposite I would be interested to get the reference.

Eugene.
 
  • #5
Well, in gtr, light bending certainly does not depend on frequency (in the geometrical optics approximation), but it's not clear to me what he has in mind.
 
  • #6
Chris Hillman said:
Well, in gtr, light bending certainly does not depend on frequency (in the geometrical optics approximation), but it's not clear to me what he has in mind.

Sorry for the late reply (have been sick). I was just wondering whether some strong kind of space-dragging effects around rotating galaxies or rotating black holes could possibly lead to a shift in frequency. Or would it only lead to a time difference ?
 
  • #7
Straightening out Light-bending (Mk1:3)

Rudi, sorry, but I don't yet understand your question. Did you take the point (already mentioned by meopemuk) that according to gtr, "light bending" (e.g. in "gravitational lensing") does not depend on the frequency of the light being bent?
 
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  • #8
Chris Hillman said:
Rudi, sorry, but I don't yet understand your question. Did you take the point (already mentioned by meopemuk) that according to gtr, "light bending" (e.g. in "gravitational lensing") does not depend on the frequency of the light being bent?

Yes, I know that light bending as such does not depend on the frequency of the light. The question is what happens in case of strong frame dragging effects, so in which the galaxy or black hole has a very large mass and high angular momentum. What would happen if we observe lensed light (from stars far beyond this large rotating mass) in this case? At one side, the light would encounter a "space rotation" in the same direction as the propagating light and at the other side the "space rotation" would be in the other direction. How would this show up in the observed light. I know the effects are small, but I'm just wondering about the physical effect.

Rudi Van Nieuwenhove
 
  • #9
This is discussed extensively in Chandrasekhar, Mathematical Theory of Black Holes.
 

FAQ: Question on gravitational lensing

1. What is gravitational lensing?

Gravitational lensing is a phenomenon in which the gravitational force of a massive object, such as a galaxy or a black hole, bends the path of light from a distant object. This results in a distortion of the appearance of the distant object, making it appear larger, brighter, or even multiple images of the same object.

2. How does gravitational lensing occur?

Gravitational lensing occurs due to the warping of space-time by massive objects. According to Einstein's theory of general relativity, massive objects create a curvature in space-time, and when light passes through this curved space-time, its path is bent, resulting in a lensing effect.

3. What are the types of gravitational lensing?

There are two main types of gravitational lensing: strong lensing and weak lensing. Strong lensing occurs when a massive object acts as a perfect lens, creating highly distorted and magnified images of the background object. Weak lensing occurs when the lensing effect is subtle and does not create multiple images, but instead causes a slight distortion in the appearance of the background object.

4. What is the significance of gravitational lensing in astronomy?

Gravitational lensing is significant in astronomy as it allows us to study and observe objects that are otherwise too distant or faint to be seen by traditional telescopes. It also helps us to understand the distribution of dark matter in the universe and the structure of galaxies.

5. Can gravitational lensing be used to study black holes?

Yes, gravitational lensing can be used to study black holes. As light passes near a black hole, its path is significantly bent, resulting in a strong lensing effect. This allows us to observe the effects of a black hole on the surrounding space and objects, providing valuable insights into their properties and behavior.

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